A ray of light from a denser medium strikes a rarer medium at an angle incidence as shown in figure. The reflected and refracted rays make an angle of 90 with each other. The angles of reflection and refraction and r and r1. The critical angle is
According to Snell’s law
But i+r=90° (Reflected and refracted rays are at an angle of 900).
⇒
⇒ μ =.
⇒ μ =
⇒
Critical angle = μ =
⇒
⇒ sin ic = tan r
⇒ ic = sin-1 (Tan r)
Therefore, the critical angle ic = sin-1(tan r)
hence the option A is correct.